Project planning is a discipline focused on determining, structuring, and scheduling the minimum work necessary to produce the outcomes defined for the scope of the project in the least amount of time under known constraints (e.g., resource availability, regulatory requirements, etc.).
Planning complex projects often requires the synthesis, scheduling, and coordination of the activities of many individuals having expertise in distinct disciplines or professions.
In most cases, each discipline or profession will have developed, and formally documented, a body of knowledge that is considered to express its best practices. Generally, each body of knowledge will describe proven and optimal approaches used to achieve specific outcomes associated with the discipline or profession (e.g., the extraction of a wisdom tooth by a dental surgeon, or the design of a user interface for a computer software application by a software engineer).
The approaches described are typically represented in the body of knowledge as a series of interdependent activities.
Combining the activities from more than one body of knowledge into a coherent and optimal whole, as represented by a project work breakdown structure (WBS) and work flow, to satisfy the set of outcomes anticipated by the scope of the project can be daunting, given that the project planner must rationalize, synthesize, and set dependencies between hundreds or thousands of discrete activities from the bodies of knowledge involved, without having the benefit of expertise in all of the disciplines or professions.